A lithographic process includes the patterned exposure of a resist allowing portions of the resist to be selectively removed, thereby exposing underlying areas for selective processing, such as etching, material deposition, ion implantation and the like. Typically, lithographic processes utilize ultraviolet light for selective exposure of the resist. In addition, charged particle beams (e.g., electron beams) have been used for high resolution lithographic resist exposure. The use of e-beam based lithography systems allows for relatively accurate control of the electron beam at relatively low power and relatively high speed.
In order to improve lithographic processes, various parameters of the electron beam from the lithography tool may be measured. Typically, parameters such as focus, astigmatism, magnification, rotation, distortion and uniformity are measured utilizing a “knife edge” technique. In this regard, the electron beam or image is scanned across a knife edge and the signal is measured utilizing either a backscatter detector or transmission detector.
The commonly implemented knife edge technique suffers from difficulties in forming a knife edge having nanometer scale sharpness and edge roughness. In addition, it is difficult to measure rotation and magnification accurately using the knife edge technique as one is limited to measuring one axis at a time. Therefore, it is desirable to provide a system and method that cures the defects of the prior art.